The field of the invention is medical imaging, and particularly, the processing of digitized medical images.
There are a number of medical imaging systems in use today which produce images in the form of digitized data arrays. Such systems may use x-rays, ultrasound, magnetic resonance, positron emission, or gamma ray emission as the modality for acquiring the image data. Regardless of the modality used to acquire it, once the image is digitized as an array of pixel intensity values, it can be processed using filters and image enhancers to improve the diagnostic quality of the image.
While the field of view of the imaging system can be controlled during image acquisition to focus on the anatomy of interest to the diagnostician, sometimes considerable background is included in the image. If the background is very bright, it can be very distracting and a hindrance to an accurate reading of the image. For example, x-ray images are often acquired with collimators placed on the machine or the patient to limit the amount of radiation reaching unintended anatomical regions. Collimators basically reduce the amount of radiation reaching the area shadowed by them. As a result, the region covered by the collimators is highly attenuated and appears bright on the final image. When such an image is viewed on a view box by a radiologist, the bright areas in the image can be quite significant and hence create a glare. This glare is very discomforting to the radiologist and can affect adversely the film reading ability of the radiologist. If the bright areas caused by the collimation can be eliminated from the image, the accuracy of reading the film can be improved.
Methods previously used to detect and remove bright background regions from medical images are either very computationally expensive, not very robust, or require considerable manual input. Such methods are described by Jiebo Luo, et al. "Collimation Detection For Digital Radiology", SPIE Vol. 3034 (1997) and the publications referred therein.